I don't know why GNU sabotages manpages. While I understand that interactive documents may be useful for seeking specific information in several thousand lines of documentation, simply replacing manpages with .info files has clear disadvantages.

First of all, info(1) is not available everywhere. While this is especially true for commercial unices, it may well apply to many open source systems, even in the Linux camp. Also, not every application in a generic unix box is a GNU application, and its documentation may not be in GNU's texinfo format. BSDs generally include info(1) and .info files for the GNU utilities they use, but programs like ls(1), awk(1) or make(1) are not GNU applications in BSD systems -- actually, GNU didn't even exist when they and their manual entries were written. Although, by definition, "GNU's not Unix", if it is Unix-like and, most especially, if it want its users to use it as they would use any other Unix system, it should allow its users to retrieve relevant information with manpages.

While there is still a handful of other serious problems with texinfo, when intended to replace manpages, I will go back to one of your first statements, and say that I disagree that .info documents provide for more well organized information. Being "navigable" doesn't at all mean that a document is well organized, and much less does it mean that it is well written and can be easily read. Even the most powerful tool can become useless or wasteful in the hands of an inept writer, and I am pretty sure that I am not the only one that knows lots of plain text documents that beat many full-featured hypertext documents regarding the same information, not only in clearness, cleverness and accuracy, but even in visual cleanness.